First dont be afraid of the HV. I got zapped at least once a week for 40 yrs.
DO respect the AC input, main B+, hoz out & damper. Those can harm
you !! Also use an isolation transformer.
So some hints.
Run the set & change channels. See if you hear or see the effect of
the tuner contacts making & breaking.
If so look to the tuner.
If not look at the IF's.
If not look for where the sound is taken off. The problem is before
the take off point. Good old time "no equipment" quick bench tests !
good luck & Merry Christmas !
73 Zeno
LFOD !